When designing the slot geometry in the stator core of electrical machines, the electrical filling factor, that is to say the quotient of copper area to slot area, is a critical parameter for describing the performance or the efficiency of the overall system. Conventional stator production methods, for example the pull-in method, allow values of from 40% to a maximum of 50% of electrical filling.
In order to further increase these values, the wires in the slot region can be compressed by a stamping process, see WO-2001054254 A1 for example. A region of over 60% of electrical filling can be achieved in the stator slots as a result. Assuming certain structural dependencies are taken into consideration (for example compact design of the winding heads, . . . ), more electrical power can be generated with relatively small structural volumes with less material being used.
Certain boundary conditions are of critical importance when technically implementing the stamping process: for example, wire crossings in the slot region can lead to pinching with a greatly reduced cross section, this leading to local overheating, and the corresponding consequences, during operation due to an increased non-reactive resistance.
High electrical filling factors are made possible particularly due to high mechanical filling in the stamping tools, and therefore the aim is to fill the stamping slot virtually to 100% taking into account the possible wire tolerances. However, this requires all the wires in the slot region to be deformed as uniformly as possible.
This requirement is not met if an expedient stamping direction is not chosen. If the wire is stamped in the radial direction (in the direction of the slot height), the wire, which is in contact with the stamping punch, will be deformed to an overproportional extent in comparison to the wire in the stamped slot base because the stamping pressure is not uniformly distributed within the slot due to mechanical friction and other influences. Purely on a calculation basis, a stamped slot filling of greater than 100% is established on the stamping punch. As a result, copper is pushed into the winding heads and therefore into the electromagnetically inactive region of the machine in the longitudinal direction of the wire. Therefore, the wire cannot be stamped in an optimum manner.